With the recent downsizing of electronic devices, the technique of evaluating the device structures is also required to have high precision. Among the evaluation techniques, especially TEM (Transmission electron Microscope) and STEM (Scanning Transmission Electron Microscope), which can focus electron beams up to the nanometer order, are effective for the high precision observation and analysis. However, these means give only projected images of three dimensional device structures, i.e., two dimensional information and cannot give information in the direction of advance of the electrons (the direction of depth of sample).
In such present circumstances, in order to generally evaluate electronic device structures having three dimensional structures, the technique of observing the samples in different sections, and the technique of three-dimensionally adjoining images observed in multi-directions (electron beam tomography), etc. are used. The former has disadvantages that a plural numbers of a sample are required, and the section makes the amount of information imperfect. The latter has disadvantages that a sample must be sectioned with a target object positioned at the center, which makes the processing time long and makes the amount of information lack.
On the other hand, techniques other than TEM are the confocal laser scanning microscopy, and the technique that the SEM (scanning electron microscopy) observation is made with focused ion beams while the processing is being made to thereby adjoin a three-dimensional structure. But these techniques are inferior to TEM and STEM in the image resolving power and are difficult to be used in evaluating fine structures.
Generally, when the universal TEM and STEM, which use the acceleration energy of about 200 kV, are used, the evaluation samples are processed in a thickness of not more than about 200 nm. This is because as the evaluation samples are thicker, the interactions between the incident electrons and the materials increase, and the incident energy is liable to be lost. The electrons which have thus lost the energy is a factor of focal blur, of the TEM images and the STEM images, and when a sample of, e.g., a micron order thickness is observed with the universal TEM and STEM described above, the images are blurred.
The electric devices have various structures and sizes, and when an evaluation sample has a thickness of the micron order, there is a risk that unnecessary information might be mixed. Such information corresponds to the information of, e.g., the insulting regions in evaluating the device regions, and the information of, e.g., the inter-layer insulating films and cover films, etc. in evaluating the interconnections. Similarly, the support films, the packing materials, etc. used in reinforcing the samples of TEM and STEM, which are irrelevant to the observation and analysis, idealistically do not function as the purposes other than the purpose of securing the mechanical strength. However, the interactions between these materials and the incident electrons cannot be hindered.
As described above, conventionally, no means of evaluating generally and with high precision the electronic device structures of three-dimensional structures have been available. For further downsizing of the electronic devices, a technique which can evaluate generally and with high precision electronic device structures, etc. of three-dimensional structures has been expected.